1. Field of the Invention
The present invention relates to a magnetic recording element mounted on, for example, a hard disk device or the like, and particularly to a thin film magnetic head which can be improved in corrosion resistance, smoothness and demagnetization near the interface between a gap layer and a lower pole layer (or a lower core layer), and a method of manufacturing the thin film magnetic head.
2. Description of the Related Art
FIG. 14 is a partial front view showing the structure of a conventional thin film magnetic head.
In FIG. 14, reference numeral 1 denotes a lower core layer made of a magnetic material such as permalloy or the like, an insulating layer 9 being formed on the lower core layer 1.
The insulating layer 9 has a trench 9a formed in the height direction (the Y direction shown in the drawing) from a surface facing a recording medium to have an internal width dimension corresponding to a track width Tw.
In the trench 9a, a lower pole layer 2 magnetically connected to the lower core layer 1, a gap layer 4, and an upper pole layer 5 magnetically connected to an upper core layer 6 are formed by plating in turn from the bottom. Furthermore, the upper core layer 6 is formed on the upper pole layer 5 by plating.
Furthermore, a coil layer (not shown in the drawing) is patterned in a spiral shape on the portion of the insulating layer 9, which is behind the trench 9a formed in the insulating layer 9 in the height direction (the Y direction).
In the inductive head shown in FIG. 14, when a recording current is supplied to the coil layer, a recording magnetic field is induced in the lower core layer 1 and the upper core layer 6. As a result, a magnetic signal is recorded on a recording medium such as a hard disk or the like by a leakage magnetic field from the gap between the lower pole layer 2 and the upper pole layer 5 magnetically connected to the lower core layer 1 and the upper core layer 6, respectively.
The gap layer 4 is made of, for example, NiP which can be plated. A NiP film is conventionally formed by electroplating using a DC current.
However, it was found that when the NiP film was grown from the interface with the lower pole layer 2 by electroplating with a DC current, the content of element P was very low near the interface. For example, it was found from the experimental results described below that the content of element P was less than 8% by mass within a distance of about 2.5 nm from the interface in the thickness direction.
In electroplating with a DC current, the density of the current supplied to the NIP film during plating has a nonuniform distribution, and the current concentrates in a certain plating surface and continuously flows through the surface. The nonuniform current distribution possibly causes a significant decrease in the content of element P near the interface because element Ni, which easily produces lattice matching with the crystalline lower pole layer 2, is epitaxially grown and crystallized. Also, the epitaxial growth of Ni worsens surface roughness at the interface.
The above-described NIP film having a very low content of element P near the interface and surface roughness exhibits low corrosion resistance and low resistance to neutral to alkali aqueous solutions. Therefore, the NIP film is readily corroded with a cleaning liquid used in the cleaning step of a slider manufacturing process to cause the problem of cracking, as shown in FIG. 15 (schematic drawing). Thus, recording properties such as an overwrite performance deteriorate.
Also, when the content of element P is decreased near the interface, the vicinity of the interface is readily magnetized, and thus the gap length G1 determined by the thickness of the gap layer 4 varies, thereby failing to manufacture a thin film magnetic head having predetermined recording properties in high yield.
Accordingly, the present invention has been achieved for solving the above problem, and an object of the present invention is to provide a thin film magnetic head which is increased in the content of element P near the interface to improve corrosion resistance and smoothness of a gap layer and promote demagnetization at the interface, as compared with a conventional magnetic head.
Another object of the present invention is to provide a method of manufacturing a thin film magnetic head which comprising forming a gap layer by electroplating with a pulsed current to suppress crystallization of element Ni due to epitaxial growth near the interface and increase the content of a nonmagnetic element (for example, element P).
In order to achieve the objects of the present invention, a thin magnetic element comprises a lower core layer, a gap layer formed on the lower core layer directly or through a lower pole layer, and an upper core layer formed on the gap layer directly or through an upper pole layer which determined a track width, wherein the gap layer is formed by plating NiP, and the content of element P is 8% by mass to 15% by mass within a distance of 10 nm from the interface with the lower pole layer or the lower core layer in the thickness direction.
Therefore, the gap layer does not have a region in which Ni is crystallized by epitaxial growth from the interface with the lower pole layer or the lower core layer in the thickness direction. Thus, in the present invention, the vicinity of the interface is in an amorphous state containing 8% by mass to 15% by mass of element P, while in a conventional magnetic head, Ni is crystallized.
In this way, the interface is brought into the amorphous state containing more element P than the conventional magnetic head, thereby improving corrosion resistance and smoothness of the gap layer. Therefore, the gap layer is not corroded with a cleaning liquid used in a cleaning step of a slider manufacturing process, and thus the problem of cracking the gap layer can be prevented, unlike the conventional magnetic head. Furthermore, the region within a distance of 10 nm from the interface in the thickness direction contains 8% by mass to 15% by mass of element P, and thus the region can be demagnetized, thereby permitting high-yield manufacture of a thin film magnetic element with a predetermined value of gap length G1.
In the present invention, the content of element P is preferably 8% by mass to 15% by mass within a distance of 40 nm from the interface.
In the present invention, the content of element P is preferably 10% by mass to 15% by mass, and more preferably 11% by mass to 15% by mass.
With the content of element P within the above range, crystallization of element Ni by epitaxial growth can be further suppressed to further improve corrosion resistance of the gap layer, and promote demagnetization near the interface of the gap layer, thereby permitting manufacture of a thin film magnetic head having good recording properties.
In the present invention, the average content of element P of the gap layer over its entire thickness is preferably 11% by pass to 15% by mass.
By controlling not only the content of element P within the distance of at least 10 nm, preferably 40 nm, from the interface, but also the average content of element P of the gap layer over its entire thickness within the above-described ranges, the corrosion resistance of the entire gap layer can be improved, and demagnetization of the entire gap layer can be promoted, thereby enabling the secure occurrence of a leakage magnetic field neat the gap layer.
The content of element P is measured by using an X-ray analysis apparatus. Since only a relative value of the content of element P can be obtained by the X-ray analysis apparatus, the content of element P obtained by the X-ray analysis apparatus is corrected to an absolute value by wet analysis. The thus-obtained value is the content of element P of the present invention.
The distance from the interface with the lower pole layer or the lower core layer is measured by using a transmission electron microscope (TEM).
In another aspect of the present invention, a method of manufacturing a thin film magnetic head, which comprises a lower core layer made of a magnetic material, and an upper core layer made of a magnetic material and opposed to the lower core layer with a gap layer provided therebetween at a surface facing a recording medium, comprises the steps of (a) forming the lower core layer by plating, (b) forming the nonmagnetic gap layer mainly composed of Ni, by electroplating with a pulsed current, directly on the lower core layer or on a lower pole layer formed on the lower core layer by plating, and (c) forming the upper core layer on the gap layer directly or through an upper pole layer by plating.
As described above, the gap layer is conventionally formed by electroplating with a DC current. However, this method causes a nonuniform current density distribution, and thus causes the current to concentrate in a certain plating surface and continuously flow through the plating surface. The nonuniform current distribution causes crystallization of Ni due to epitaxial growth near the interface with the lower pole layer or the lower core layer. As a result, the content of a nonmagnetic element (for example, element P) near the interface is abruptly decreased to deteriorate corrosion resistance and demagnetization of the vicinity of the interface.
Therefore, the present invention uses electroplating using a pulsed current instead of the DC current.
Namely, a current control element is repeatedly turned on and off to provide a time to pass the current, and a null time to pass no current. By providing the null time to pass no current, the nonuniformity of the current density distribution in plating can be ameliorated to slowly form the gap layer, as compared with a conventional electroplating with the DC current.
Therefore, crystallization of Ni due to epitaxial growth near the interface is suppressed to permit the plating formation of the gap layer in an amorphous state containing a proper amount of a nonmagnetic element near the interface. Therefore, the gap layer having excellent corrosion resistance and smoothness can be formed, and demagnetization near the interface can be promoted.
In the present invention, in the step (b), preferably, the gap layer is first formed by plating to a predetermined thickness using a pulsed current having a predetermined current density, and then the residue of the gap layer is formed by plating with a pulsed current having a higher current density than the predetermined current density.
As described above, the current density in plating is first low at the interface to slow down growth by plating, thereby suppressing crystallization of Ni due to epitaxial growth to form an amorphous state containing a proper amount of a nonmagnetic element. Then, the current density is increased to speed up growth by plating, thereby permitting the formation of the gap layer within a short time. In the stage in which the current density is increased, the gap layer, which has been formed by plating growth with the low current density, is in the amorphous state, and thus the gap layer to be formed on the amorphous gap layer by plating growth with the increased current density is also in the amorphous state while containing a proper amount of nonmagnetic element. Therefore, in the present invention, the whole gap layer can be put into the amorphous state containing a proper amount of nonmagnetic element.
In the present invention, the predetermined current density is 1.5 mA/cm2 to 3.0 mA/cm2, and the pulsed current having this current density is preferably used for forming the gap layer by plating up to a thickness of 10 nm.
In the present invention, more preferably, the gap layer is first formed by plating to a thickness of 40 nm.
With the current density in the above numerical range, the gap layer is slowly grown by plating near the interface to form an amorphous film containing a proper amount of nonmagnetic element, thereby appropriately suppressing crystallization of element Ni due to epitaxial growth. With the current density lower than the above value, the plating growth rate is excessively low, and thus the gap layer is undesirably little grown by plating. While with the current density higher than the above value, the plating growth rate is excessively high, and thus the nonmagnetic element is less contained in the film to undesirably cause crystallization of Ni.
When the gap layer is formed by plating NiP, the content of element P in the film of 10 nm thick can be set to 8% by mass to 15% by mass. Preferably, the content of element P in the film of 40 nm thick can be set to 8% by mass to 15% by mass.
In the present invention, the residue of the gap layer is preferably formed by plating with the pulsed current having a current density of 8.5 mA/cm2 to 11.0 mA/cm2. In plating the residue of the gap layer, the current density is increased from the initial current density to speed up plating growth, thereby permitting the formation of the gap layer within a short time. Even when the residue of the gap layer is formed by plating with the pulsed current having the high current density, the gap layer previously formed is amorphous, and thus the residue of the gap layer can be formed in the amorphous state containing a proper amount of nonmagnetic element. When the gap layer is composed of NiP, the average content of element P of the gap layer over its entire thickness can be set to 11% by mass to 15% by mass.
In the present invention, the gap layer is formed by plating any one of Nixe2x80x94P, Nixe2x80x94W, Nixe2x80x94Pxe2x80x94Mo, and Nixe2x80x94Pxe2x80x94W.
Namely, the electroplating process using the pulsed current can suppress crystallization of Ni due to epitaxial growth near the interface, permitting the plating formation of the gap layer having excellent corrosion resistance and smoothness, and improved demagnetization.